Cell Phone Data Tracks Puerto Rico Migration

Posted June 14, 2018

How many people have left Puerto Rico since Hurricane Maria and where have they gone? How many have returned to the Island?

The Census Bureau has no answers to these questions yet; their last population estimate for Puerto Rico is for July of 2017. Data on the subject has relied on information that can’t give a complete answer.

School enrollment counts, airplanes leaving Puerto Rico, the number of people receiving services from nonprofits — all of these data sources have problems. Household numbers have to be extrapolated from those using schools and nonprofit services. Since this type of information is not publicly reported, estimates may be casual and inaccurate.

What’s more, the data may not be collected accurately. For example, students from Puerto Rico may be classified as “newcomers” — immigrants — even though they have been in U.S. school systems in Puerto Rico, and be missed in counts because of that. People traveling on airplanes may have many different reasons for their travel, and it is not possible to know those reasons.

Individuals are almost certainly left out of reports like these. Some reports may then over-correct by adding a margin to account for the likely underreporting.

Some figures have been the result of statistical modeling based on assumptions about people’s future decisions.

Another way to track population movement

A European data company called Teralytics took another approach. Using data on 500,000 cell phones, they saw where people in Puerto Rico before the hurricanes hit took their phones afterwards. Since most adults and many teens own cell phones and carry those phones at all times, this provided more accurate geolocation information.

Teralytics was able to show where cell phones traveled from Puerto Rico following the hurricanes, shown in red below. Cell phones traveling to Puerto Rico are shown in blue.

From October to February, Teralytics says, 12% of the population left Puerto Rico, and half returned. Since February, the number of people who have returned to Puerto Rico is greater than the number that left during that time.

Puerto Rico’s ability to maintain a population of workers in the territory is one of the most important wild cards in economic forecasts for the Island. More accurate data can be beneficial for this purpose, as well as for future planning for natural disasters and for funding in States where evacuees went and may stay.

Privacy issues

Cell phones have been used in other countries to understand migration patterns (resulting from wars, for example) and allocate resources effectively.

In the U.S., laws on the subject differ from one State to another. Teralytics says that the data is completely stripped of all personally identifiable information. Their privacy policy is similar to the policies of other tech companies, and emphasizes the anonymity of the aggregate data they use.

Jose Aponte-Hernández, a member of the Puerto Rico House of Representatives, expressed concern over the privacy of the cell phones’ owners, saying that Teralytics is using personal information “to track and hunt U.S. citizens exercising their democratic right to freely travel within our nation’s borders.”